EP0813253A2

EP0813253A2 - Thermoelectric generator

Info

Publication number: EP0813253A2
Application number: EP97109407A
Authority: EP
Inventors: Shoko Miyake; Hisaaki Gyoten
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1996-06-11
Filing date: 1997-06-10
Publication date: 1997-12-17
Also published as: JPH09329058A; EP0813253A3; US5917144A

Abstract

A thermoelectric generator using catalytic combustion heat of fuel gas as a heat source, has a construction wherein a thermoelectric element or a planar electric generation unit comprising thermoelectric elements has a construction held between the thermal input part and the heat radiation part, having fuel gas supply means and means for mixing fuel gas with air, and having a structure that the combustion heat can be directly supplied to the thermoelectric element by burning the mixed gas of fuel with air in a catalyst part arranged in said thermal input part, said thermal input part having a heat conductive end plate and a catalyst part which are in contact with the thermoelectric element, the face opposite to said thermoelectric element of said heat conductive end plate having a structure of convex and concave configuration, and said catalyst part being constituted in said convex and concave configuration surface.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thermoelectric generator utilizing as heat source the heat of catalytic combustion. Also, the present invention relates to the constitution of a thermoelectric generator usable as an electric source for outdoor application.

2. Related art of the Invention

Conventionally, as the power source for outdoor use, batteries and engine electric generators have mainly been used. However, in case of a battery, due to the time required for charging, it has been inconvenient for continuous use outdoors. The engine generators using gasoline as a fuel has large capacity for generating electricity, but as it shows large sound in operation, it is not suited for example for the power source for speaker or the like, and its use is limited. Accordingly, as the power source for outdoor use which is safe, silent in sound, and adaptable to continuous use with good facility for use, a thermoelectric generator is recommended.
The thermoelectric generator which performs direct conversion of heat to electricity by utilizing the thermoelectric power which is produced when temperature differences are given to thermoelectric material is noted with attention as emergency power source, portable power source, power source for remote place, device for recovering waste heat, etc. As the heat sources for these electric generators there are used heat of combustion, heat of catalyst combustion, heat of exhaust gas, etc., of which the heat utilizing catalytic combustion heat has characteristics such that the temperature adjustment can be easily made by adjustment of flow rate of fuel gas, and combustion heat can be thermally inputted efficiently to the electric generating part by making planar combustion.
Conventionally, there has been known as a thermoelectric generator utilizing catalytic combustion as heat source an apparatus which was made public in Japanese Patent Publication (Unexamined) No. 85973/19xx.
Its constitution includes, as shown in FIG. 10, a combustion chamber 22 having inside a net-like catalyst holder cylinder 21, a thermocouple 23, and a fin 24 for thermal discharge, with the high temperature side and the low temperature side of the thermocouple are fixed respectively to the outer wall of the combustion chamber 22 and the fan 24 for heat discharge.
However, the thermoelectric conversion efficiency of the generator utilizing the catalytic combustion as illustrated as heat source is generally low at 4%. Accordingly, if the performance of the thermoelectric element is unchanged, in order to improve efficiency, there is required a constitution to utilize the catalytic combustion more efficiently. Namely, there is required a constitution to reduce the rate of the heat discharged without being utilized for thermoelectric conversion out of the formed catalytic combustion heat. In the generator of the constitution as in FIG. 10, because the exhaust gas of high temperature at about 250 - 600°C is discharged from the combustion chamber, the generator involves problems of safety and convenience of use, especially in case of the generator for civil use.
An object of the first invention is to provide, in consideration of such task of the conventional thermoelectric generator, a thermoelectric generator using catalytic combustion heat as heat source, with which efficient thermal input of catalytic combustion heat is made possible and the temperature of the exhaust gas is reduced.
Furthermore, in case the end use is limited to the outdoor use, realization of efficient thermal input along with more compact shape and practical, i.e., conveniently usable, power source has to be considered.
Accordingly, an object of the second invention is to provide a thermoelectric generator using catalytic combustion heat as heat source, with which efficient thermal input of catalytic combustion heat is made possible, and to provide compact and practical constitution of the thermoelectric generator.
Furthermore, an object of the third invention is to provide a thermoelectric generator having compact and high performance air cooling type heat discharge system.
A thermoelectric generator of the present invention using catalytic combustion heat of fuel gas as a heat source, has a construction wherein a thermoelectric element or a planar electric generation unit comprising thermoelectric elements has a construction held between the thermal input part and the heat radiation part, having fuel gas supply means and means for mixing fuel gas with air, and having a structure that the combustion heat can be directly supplied to the thermoelectric element by burning the mixed gas of fuel with air in a catalyst part arranged in said thermal input part, said thermal input part having a heat conductive end plate and a catalyst part which are in contact with the thermoelectric element, the face opposite to said thermoelectric element of said heat conductive end plate having a structure of convex and concave configuration, and said catalyst part being constituted in said convex and concave configuration surface.
A thermoelectric generator of the present invention using catalytic combustion heat of fuel gas as a heat source, is provided with a pair of thermoelectric elements or planar electric generation units comprising thermoelectric elements held between a thermal input part and a heat radiation part, in a structure to share said thermal input part, having fuel gas supply means, and means for mixing a fuel gas with air, and having a structure of being capable of directly supplying the combustion heat to said thermoelectric element by burning the mixed gas of fuel with air in a catalyst part arranged in said thermal input part, characterized in that said thermal input part comprises a heat conductive end plate and a catalyst part, a surface opposite to said thermoelectric element of said heat conductive end plate has convex and concave shaped structure, and said catalyst part is constituted on said convex and concave shaped surface.
A thermoelectric generator of the present invention using catalytic combustion heat of fuel gas as a heat source, has a construction wherein a thermoelectric element or a planar electric generation unit comprising thermoelectric elements has a construction held between the thermal input part and the heat radiation part, having fuel gas supply means and means for mixing fuel gas with air, and having a structure that the combustion heat can be directly supplied to the thermoelectric element by burning the mixed gas of fuel with air in a catalyst part arranged in said thermal input part, characterized by having means for thermal recovery and simultaneously reducing the temperature of exhaust gas by making heat exchange between the exhaust gas from the thermal input part and the fuel before being supplied to said thermal input part.
A thermoelectric generator of the present invention using catalytic combustion heat of fuel gas as a heat source, has a construction wherein a thermoelectric element or a planar electric generation unit comprising thermoelectric elements has a construction held between the thermal input part and the heat radiation part, having fuel gas supply means and means for mixing fuel gas with air, and having a structure that the combustion heat can be directly supplied to the thermoelectric element by burning the mixed gas of fuel with air in a catalyst part arranged in said thermal input part, said means for mixing fuel gas with air being constituted by a nozzle for jetting a fuel gas and a throat part for sending the jetted fuel gas and the air mixed in the form of being involved in the fuel gas into the thermal input part, and being provided with means for carrying out thermal recovery by heat exchange between the exhaust gas from said thermal input part and the mixed gas passing in the throat part, and for reducing the temperature of the exhaust gas.
A thermoelectric generator of the present invention using catalytic combustion heat of fuel gas as a heat source, has a construction wherein a thermoelectric element or a planar electric generation unit comprising thermoelectric elements has a construction held between the thermal input part and the heat radiation part, having fuel gas supply means and means for mixing fuel gas with air, and having a structure that the combustion heat can be directly supplied to the thermoelectric element by burning the mixed gas of fuel with air in a catalyst part arranged in said thermal input part, said means for mixing fuel gas with air being constituted by a nozzle for jetting a fuel gas and a throat part for sending the jetted fuel gas and the air mixed in the form of being involved in the fuel gas into the thermal input part, characterized in that the air to be mixed in the form of being involved in a fuel gas is the air which is heat exchanged by the exhaust gas from said thermal input part.
A thermoelectric generator of the present invention comprises a thermal input part using the catalytic combustion heat of fuel gas as a heat source, a heat radiation part having a heat conductive container whose at least a part of the outer surface is of a fin shape, more than a pair of planar electric generation units held between the outer wall of said thermal input part and the inner wall of said heat radiation part, utilizing a thermoelectric element, fuel gas supply means including a fuel tank, and mixing means for mixing a fuel gas with air, said fuel gas supply means and said mixing means being installed in a heat conductive container in said heat radiation part, characterized by directly supplying the combustion heat to the thermoelectric element of said thermoelectric generation unit by burning the mixed gas of fuel with air in a catalyst part disposed in said thermal input part, and at the same time air cooling or water cooling said heat radiation part.
A thermoelectric generator of the present invention comprises a thermal input part using the catalytic combustion heat of fuel gas as a heat source, a heat radiation part having a heat conductive container whose at least a part of the outer surface is of a fin shape, more than a pair of planar electric generation units held between the outer wall of said thermal input part and the inner wall of said heat radiation part, utilizing a thermoelectric element, a fuel tank, a fuel gas transporting means, and mixing means for mixing a fuel gas with air, said mixing means being installed in a heat conductive container in said heat radiation part, said fuel tank being freely installed in or out of the container, and connected to said mixing means through said fuel gas transporting means, characterized by directly supplying the combustion heat to the thermoelectric element by burning the mixed gas of fuel with air in a catalyst part disposed in said thermal input part, and air cooling or water cooling said heat radiation part.
A thermoelectric generator of the present invention comprises a thermal input part using the catalytic combustion heat of fuel gas as a heat source, a heat radiation part constituted by a heat conductive plate whose at least a part of the outer surface is of a fin shape, a cooling water container provided outside said heat radiation pat, more than a pair of planar electric generation units held between the outer wall of said thermal input part and the inner wall of said heat radiation part, utilizing a thermal element, fuel gas supply means including a fuel tank , and mixing means for mixing a fuel gas with air, said fuel gas supply means and said mixing means being installed in a heat conductive container in said heat radiation part, characterized by directly supplying the combustion heat to said thermoelectric element of said thermoelectric generation unit by burning the mixed gas of fuel with air in a catalyst part disposed in said thermal input part, and water cooling said heat radiation part by supplying water to said cooling water container.
A thermoelectric generator of the present invention comprises a thermal input part for inputting heat, a heat radiation part having a fin part and a fan, an electric generation unit held between said heat radiation part and said thermal input part for carrying out thermoelectric conversion by utilizing a thermoelectric element, and fuel supply means for supplying fuel, being designed to supply heat directly to the high temperature side of said thermoelectric element, simultaneously air cool the radiation part which is in contact with the radiation side of said thermoelectric element and carry out thermoelectric generation, characterized in that the whole or a part of said fan is stored in the fin part of said radiation part.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a thermoelectric generator according to the first embodiment of the first invention;
FIG. 2 is a block diagram of a thermoelectric generator according to the second embodiment of the first invention;
FIG. 3 is a block diagram of a thermoelectric generator according to the third embodiment of the first invention;
FIG. 4 is a block diagram of a catalyst part in the thermoelectric generator according to the third embodiment of the first invention;
FIG. 5 is a block diagram of a thermoelectric generator according to the third embodiment of the first invention;
FIG. 6 is a block diagram of a thermoelectric generator according to the fourth embodiment of the first invention;
FIG. 7 is a block diagram of a thermoelectric generator according to the fourth embodiment Of the first invention;
FIG. 8 is a block diagram of a thermoelectric generator according to the fourth embodiment of the first invention;
FIG. 9 is a block diagram of a thermoelectric generator according to the fourth embodiment of the first invention;
FIG. 10 is a block diagram of conventional thermoelectric generator;
FIG. 11 is a block diagram of a thermoelectric generator according to the first embodiment of the second invention;
FIG. 12 is a block diagram of a thermal input part according to the first embodiment of the second invention;
FIG. 13 is a block diagram of a thermoelectric generator according to the second embodiment of the second invention;
FIG. 14 is a block diagram of a thermoelectric generator according to the third embodiment of the second invention;
FIG. 15 is a block diagram of a thermoelectric generator according to the first embodiment of the third invention; and
FIG. 16 is a block diagram of a thermoelectric generator according to the second embodiment of the third invention.

Description of marks:

1: Thermoelectric element or planar electric generation unit
2: Radiating part
3: Thermal input part
4: Twin
5: Fan
6: Heat conductive end plate
7: Catalyst part
8: Side wall
9: Heat insulating material
10: Fuel tank
11: Nozzle
12: Throat part
13: Gas inlet
14: Exhaust port
15: Metal carried catalyst
16: Metal thin plate
17: Precious metal catalyst carried ceramic fine powder
18: Exhaust gas flow path
19: Flow path
20: Evaporation chamber
21: Catalyst holding tube
22: Combustion chamber
23: Thermoelectric element
24: Fin for radiation
31: Thermoelectric element or planar generating unit
32: Radiation part
33: Thermal input part
34: Heat conductive end plate
35: Catalyst part
36: Exhaust gas pipe
37: Fuel tank
38: Nozzle
39: Throat part
40: Cooling water container
41: Gas tube
51: Planar electric generation unit (thermoelectric element)
52: Fin part
53: Thermal input part
54: Fan
55: Combustion chamber
56: Combustion part
57: Fuel tank
58: Nozzle
59: Throat part
60: Radiation part
61: Motor part
62: Heat insulating layer

PREFERRED EMBODIMENTS

(A)

Hereinafter, the first embodiment of the present invention will be illustrated with reference to Figs. 1 to 9.

(Embodiment 1)

FIG. 1 is a sectional view showing the constitution of the thermoelectric generator according to Embodiment 1, wherein the upper drawing is a cross-sectional view, and the lower drawing is a vertical sectional view. In FIG. 1, the part 1 is a thermoelectric element or planar electric generating unit made by connecting in series a plurality of thermoelectric elements, being held between the radiating part 2 and the thermal input part 3. The radiation part 2 is constituted by an aluminum fin 4 for radiation and a fan 5. The heat input part 3 comprises a heat conductive end plate 6 and a catalytic part 7. The heat conductive end plate 6 has a configuration of comb shaped heat exchange fin so that the face opposite to the joining face with the thermoelectric element 1 has increased surface area. Accordingly, for the heat conductive end plate 6 it is desirable to use an aluminum die cast which has good processability. The catalyst part 7 is installed in a manner to cover the surface of the heat conductive end plate 6 on the side of the comb shaped heat exchange fin side. The part 8 is a side wall, and 9 is a heat insulating material such as alumina wool. The part 10 is a fuel tank for holding the fuel such as butane, being connected to the thermal input part 3 through the nozzle 11 and the throat part 12 which are the mixing means of fuel gas with air. Of the thermal input part, the part 13 is a gas flow inlet, and 14 is an exhaust port.
With respect to the thermoelectric generator constituted as above, the operation thereof is explained below. The fuel jetted from the nozzle 11 becomes a mixed gas involving the surrounding air, and passes through the throat part 12 to be sent into the thermal input part 3 from the gas flow inlet. The charged mixed gas shows catalytic combustion on the catalyst part 7 in the thermal input part 3, after which it is discharged outside the generator from the exhaust port 14. The catalytic combustion heat obtained in the thermal input part 3 reaches the high temperature side surface of the thermoelectric element 1 through the heat conductive end plate 6. As the low temperature side of the thermoelectric element 1 is in contact with the radiation part 2, there occurs temperature difference between the high temperature side and the low temperature side of thermoelectric element 1 and electric generation is performed by thermoelectric power.
According to this embodiment, by using a heat conductive end plate of comb shaped structure, a thermal input part of a type integral with the heat exchanger can be constituted, and accordingly, the catalytic combustion heat can be efficiently inputted to the high temperature side surface of the thermoelectric element. Also, as the heat conductive end plate and the catalyst part are in mutual contact, excessive rise of the surface temperature of the combustion part can be prevented to make it possible to realize a constitution suited for the heat resistance of the thermoelectric element.
When the thermal input part is formed into such constitution as to surround the catalyst part which is formed on the surface side of the comb shaped fin input of each heat conductive end plate, the surface areas of the catalyst part and the fin can be doubled without changing the volume of the thermal input part. Therefore, it is possible to constitute a thermal input part of higher density. Concrete example of it is shown in the next passage.

(Embodiment 2)

In FIG. 2, there is shown a constitution of a thermoelectric generator wherein a thermoelectric element or a pair of planar electric generator units comprising thermoelectric elements are bonded to both sides of the thermal input part, and snapped between the thermal input part and the radiation part.
In FIG. 2, the construction of the heat conductive end plate 6 of the thermal input part 3 is the same as that of Embodiment 1, but in the style of the present embodiment a pair of heat conductive end plates 6 are combined in a manner that the comb shaped fin side surfaces of a pair of heat conductive end plates 6 are opposed, and the catalyst part 7 is formed on said comb shaped fin. On the surface opposite to the comb shaped fin side of each heat conductive end plate 6 there is set up a planar electric generation unit 1 comprising a thermoelectric element. As a planar electric generation unit 1, there is used one having a construction wherein a plurality of thermoelectric elements arranged on a plane are connected in series. The construction of the radiation part 2 is similar to that of Embodiment 1, wherein the radiation part 2 is installed in a manner to hold these planar generating units 1 with the thermal input part 3. Since the operation of the generator of this constitution is the same as that of Embodiment 1, description thereof is omitted.
As shown in FIG. 2, by arranging the combustion chamber which is a thermal input part 3 into such construction as to have the heat conductive end plates positioned in opposite manner, the surface area of the heat exchange fins can be increased simultaneously with the increase in the catalytic combustion area, with the volume of the combustion chamber left unchanged. Thus, a higher density heat source can be formed. Furthermore, by making the generation unit opposed type by installing the generation units on both sides of the thermal input part, combustion heat discharged outside the generator from the surface of the thermal input part can be largely decreased, thereby permitting the thermal input in good efficiency. As a result, it becomes possible to constitute a compact thermoelectric generator with greatly improved generation efficiency.

(Embodiment 3)

FIG. 3 is a block diagram of a thermoelectric generator in the case of using a metal carried catalyst 15 as a catalyst part. The catalyst part 15 has a construction wherein ceramic fine powder 17 such as alumina carrying a precious metal catalyst of platinum or the like is applied to the surface of a heat-resistant metal thin plate 16 having a thickness of no more than 0.5 mm. For the heat resistant metal thin plate 16 the material having good processing property such as SUS plate may be used. Other constitution and operation are the same as those of Embodiment 1.
By using the catalyst part 15 of the constitution as in FIG. 3, a high performance catalyst part can be produced at a low cost. Furthermore, in case of the degradation the catalyst part can be simply replaced to improve practical utility.
Between the heat resistant metal thin plate 16 and the fin part 6b of the end plate 6, a gap is provided. By this gap there can be obtained an effect of the catalyst temperature not to be excessively lowered and good heat conductivity.
An example where a metal carrier catalyst having a rectangular wave shape at the end of the gas flow inlet side is used as a metal carrier catalyst 15 is shown in FIG. 4. In FIG. 4, the right side figure is a cross-sectional view, and the left side figure is a vertical section taken from the right side thereof. A gas flows in from the right side of the left figure (the right side here practically corresponds to the lower part). A metal carrier catalyst 15 is formed on a part of the fin side surface of the heat conductive end plate 6. That is to say, in the left side figure, on the base plate part 6a of the end plate 6, there are provided in projection 8 fins 6b of the end plate 6 in lateral direction. And, on the uppermost fin part 6b the catalyst is formed only to about 2/3 part to the left, on the directly lower fin part 6b the catalyst 15 is wholly formed, and on the next lower fin part 6b the catalyst 15 is formed only to about 2/3 part to the left. The succeeding fin parts 6b are of the similar state. On the other hand, as to the end plate base plate 6a between those fins 6b there exist alternately the portions covered wholly with the catalyst 15 and the portions covered only to about 2/3 to the left part.
According to the constitution of the catalyst part 15 as in FIG. 4, because the catalyst part 15 on the gas inlet side becomes less, the catalyst combustion on the inflow side which tends to become high temperature can be dispersed, so that the heat can be conducted without unevenness to the high temperature side surface of the thermoelectric element through the heat conductive end plate. Accordingly, the difference of thermoelectric powers between the thermoelectric material chips constituting the thermoelectric elements can be dissolved, and the damage or deterioration of the elements caused by the local excess of the heat resistant temperature of the element can be prevented, with the result that the efficiency and durability of the generator can be improved.
As to the shapes of the catalyst part end, there may be corrugated, V-shaped, etc. besides the rectangular shape as illustrated in the left view of FIG. 4.
Further, FIG. 5 is a sectional view of a thermoelectric generator in the case where the thickness of the heat conductive end plate 6 is changed so as to become larger in the vicinity of the gas flow inlet 13 and smaller in the vicinity of the exhaust port 14. The upper view is a cross-section, and the lower view is a vertical section.
In the constitution of FIG. 1, due to the catalytic combustion heat which is formed in concentration in the vicinity of the end of the catalyst part 7 on the gas flow inlet 13 side, temperature distribution is formed on the heat conductive end plate 6 in the gas flow direction. However, by using a heat conductive end plate 6 of the constitution as in FIG. 5, the temperature distribution is dissolved in the thermal input surface and heat can be conducted without unevenness to the high temperature side surface of the thermoelectric element. In other words, the thickness of the base part 6a of the end plate 6 is made thicker on the inflow side and thinner on the outflow side.
Because of the above, the difference of thermoelectric powers between the thermoelectric material chips constituting the thermoelectric element can be dissolved, leading to the improvement of the electric generation efficiency of the element. Also, it is possible to prevent damage or deterioration of the element caused by local excess of the heat resistant temperature of the element, and the durability of the generator can be improved.
Furthermore, though not illustrated, when the catalyst part 15 is reduced to half area, namely, when the catalyst part on the inflow side 15 is made not to cover either the base part 6a of the end plate 6 or the fin part 6b, the position on which the catalytic combustion occurs in concentration comes to nearly the central part of the joint face with the thermoelectric element or planar electric generation unit. In case of forming the catalyst part 15 in such manner, the thickness of the base plate 6a of the heat conductive end plate 6 may be so set as to become the largest in the neighborhood of the position of catalytic combustion near the center and smaller toward both ends of the end plate 6.

(Embodiment 4)

FIG. 6 is a sectional view showing the constitution of the thermoelectric generator according to Embodiment 4. In FIG. 6, the construction wherein a planar electric generating unit 1 made by connecting in series a thermoelectric element or a plurality of thermoelectric elements is held between the heat radiation part 2 and the heat input part 3 is the same as in Embodiment 1. On the outer surface of the side wall 8 of the thermal input part 3 there is constituted an exhaust gas flow path 18, and on further outside thereof there are the fuel tank 10, evaporation chamber 20, flow path 19, fuel gas jetting nozzle 11, and throat part 12, which are connected with the inside of the thermal input part 3. For the side wall 8 of the thermal input part 3 of this constitution, use of material having good heat conductivity such as aluminum is preferable.
With respect to the thermoelectric generator constituted as above, the operation thereof is described. The fuel jetted from the nozzle 11 becomes a mixed gas involving the circumferential air, passes through the throat part 12, and is sent into the thermal input part 3. The heat obtained on catalytic combustion of the mixed gas sent in on the catalyst 7 in the thermal input part 3 is utilized for electric generation by the thermoelectric element 1 in the same manner as in Embodiment 1. On the other hand, the exhaust gas produced on catalytic combustion passes through the exhaust gas flow path 18 from the exhaust port 14, and, coming into contact with the outer surface of the side wall 8 of the thermal input part 3 in the exhaust gas flow path 18, a fuel gas tank 10, an evaporation chamber 20, a flow path 19, and a throat pat 12, and is discharged outside the generator while carrying out heat exchange.
According to this embodiment, by making heat exchange between the exhaust gas from the thermal input part 3 and the fuel gas in the tank 10, flow path 18, evaporation chamber 20, and throat part 12, a part of the discharged catalyst combustion heat can be recovered to bring the mixed gas before combustion to high temperature. Because of this, the calorific power to the amount of gas used increases and the efficiency of thermoelectric generator can be improved. Moreover, the temperature of the high temperature exhaust gas at about 250 - 600°C can be reduced, and practical thermoelectric generator extensively applicable to civil use can be constituted.
In FIG. 7, as the means for cooling the exhaust gas simultaneously with thermal recovery, there is shown a thermoelectric generator constituted to make heat exchange between the exhaust gas from the thermal input part 3 and the liquid fuel in the fuel tank 10. The electric generator of FIG. 7 has a structure of a pair of generating units 1 holding a thermal input part 3 to be arranged in opposed state, in which an exhaust gas flow path 18 is set in a manner to surround the fuel tank 10. In the present embodiment, the fuel warmed in the fuel tank 10 is further warmed by the heat discharged from the side surface of the thermal input part 3 in the flow path 19 set to run along the side surface of the thermal input part 3 and evaporated, and sent to the nozzle 11.
In the constitution as in FIG. 7, by the heat exchange between the liquid fuel in the fuel tank 10 and the exhaust gas from the thermal input part 3, evaporation of fuel is accelerated to make it possible to constitute more efficient, practical, and compact thermoelectric generator.
In FIG. 8, there is shown as means for cooling exhaust gas simultaneously with heat recovery, a thermoelectric generator constituted to make heat exchange between the exhaust gas from the thermal input part 3 and the fuel gas and air mixed gas which pass through the throat part 12.
The generator of FIG. 8 has a structure made by holding the thermal input part 3 with a pair of generating units 1 in opposed state, wherein the exhaust gas flow path 18 is set so that the exhaust gas from the thermal input part 3 passes through the space between the heat conductive end plate 6 on both faces of the thermal input part 3 and the generating unit 1, comes into contact with the surface of the slot part 12, and then is discharged outside from the generator.
In the constitution as shown in FIG. 8, there can be constituted a compact generator furnished with the means for efficiently recovering the exhaust heat and simultaneously reducing the exhaust gas temperature by making heat exchange between the exhaust gas and the heat conductive end plate 6 and mixed gas before combustion.
FIG. 9 shows a thermoelectric generator constituted to make heat exchange between the exhaust gas from the thermal input part 3 and the air before being mixed with the fuel gas as the means for cooling the exhaust gas simultaneously with thermal recovery. The electric generator of FIG. 9 has a structure made by holding the thermal input part 3 with a pair of generating units 1 in opposed state, wherein the exhaust gas flow path 18 is set so that the exhaust gas from the thermal input part 4 passes through the space between the heat conductive end plate 6 on both faces of the thermal input part 4 and the generating unit 1, and then is discharged outside from the generator. A part of the exhaust gas flow path 18 has such construction that fins are formed on both sides or one side so as to make heat exchange between the high temperature exhaust gas in the flow path and the air in the surrounding of the flow path. The air which has been heat exchanged here is mixed with the fuel gas jetted from the nozzle 11 and sent into the throat part 12.
In the constitution as shown in FIG. 9, there can be constituted a compact generator provided with such means that, by carrying out heat exchange between the exhaust gas and the heat conductive end plate 6 and pre-combustion air, the exhaust heat can be efficiently recovered, and the exhaust gas temperature can be lowered.
If, in the generator of the constitution as shown in any of Figs. 1 to 9, an L-shaped throat is used as means for sending a mixed gas into the thermal input part, a more compact generator can be constituted.
As described above, according to the first invention, there can be provided a constitution of a compact, highly efficient thermoelectric generator with which the thermal input can be made in higher density in a thermoelectric generator having the catalytic combustion heat as heat source.
Also, it is possible to provide a constitution of a compact and practical generator which is provided with such means as to recover exhaust heat and utilize it for improving the efficiency of the generator and also to reduce the exhaust gas temperature.

(B)

Next, each embodiment of the second invention is explained with reference to FIG. 11 to FIG. 14.

(Embodiment 1)

FIG. 11 is a sectional view showing the constitution of the thermoelectric generator according to Embodiment 1. FIG. 12 is an enlarged view of the thermal input part 33 thereof. In FIG. 11, the part 31 is a pair of thermoelectric elements or a planar electric generating unit made by connecting in series a plurality of thermoelectric elements, being pinched between the radiating part 32 and the thermal input part 33 and set on both sides of the thermal input part 33. The radiating part 32 is constituted by an aluminum rectangular parallelepiped type container having fin shape on the outside of the four sides. The heat input part 33 is formed, as shown in FIG. 12, in a form that a pair of heat conductive end plates 34 are opposed to surround a catalytic part 35 formed on the surface of the comb shaped fin side of each heat conductive end plate 34. The heat conductive end plate 34 preferably is made of aluminum die cast which has good processing property. The catalyst part 35 is installed in a manner to cover the surface of a comb shaped heat exchange fin of heat conductive end plate 34. The catalyst part 35 is installed in a manner to cover the surface of the heat conductive end plate 34 on the side of the comb shaped heat exchange fin side. For the catalyst part 35 there may be used a heat resistant metal thin plate having a thickness of no more than 0.5 mm made by applying ceramic fine powder such as alumina carrying a precious metal catalyst such as platinum thereto. As a heat resistant metal thin plate, one having good processability such as SUS plate may be used. The part 7 is a fuel tank, for which the commercialized butane gas cylinder for cassette burner is used straightly. The fuel tank 37 is connected to the thermal input part 33 through the nozzle 38 and the throat part 39 which are the mixing means of fuel gas with air. The thermal input part 33, being provided with an exhaust gas pipe 36, is led to a part outside the container from the top face of the radiation vessel.
With respect to the thermoelectric generator constituted as above, the operation thereof is explained below. The fuel jetted from the nozzle 38 becomes a mixed gas involving the air from the upper face of the radiation part, and passes through the throat part 39 to be sent into the thermal input part 33 from the gas flow inlet. The charged mixed gas shows catalytic combustion on the catalyst part 35 in the thermal input part 33, after which it is discharged outside the generator by the exhaust gas pipe 36. The catalytic combustion heat obtained in the thermal input part 33 reaches the high temperature side surface of the thermoelectric element 31 through the heat conductive end plate 34. As the low temperature side of the thermoelectric element 31 is in contact with the radiation part 32, there occurs temperature difference between the high temperature side and the low temperature side of thermoelectric element 31 and electric generation is performed by thermoelectric power. On the outside surface of the radiation part 32, the larger electromotive force can be obtained by cooling with water rather than by cooling with air. For water cooling, the upper face of the generator may be exposed to air and the generator dipped in water.
When the generator of this embodiment is driven, about 2 minutes' time is necessary before the output is stabilized, but thereafter generation is continued until the fuel gas is exhausted. When the commercialized butane gas for cassette burner is used as a fuel gas, about 8 - 11 hours' generation is possible with a cylinder (250 g). On constitution of a generator of about 1 liter body, the output was about 20 W (water cooling). Accordingly, on constitution of a generator of 2 liter body, the output in water cooling was more than 35 W.
According to this embodiment, by using a heat conductive end plate of comb shaped structure, a thermal input part of a type integral with the heat exchanger can be constituted, and accordingly, the catalytic combustion heat can be efficiently inputted to the high temperature side surface of the thermoelectric element. Also, as the heat conductive end plate and the catalyst part are in mutual contact, excessive rise of the surface temperature of the combustion part can be prevented to make it possible to realize a constitution suited for the heat resistance of the thermoelectric element.
Also, as the gas tank is contained in the heat radiation vessel, the fuel supply part can be kept at high temperature, and it becomes possible to send the fuel gas of high temperature and high pressure into the combustion chamber, and combustion in good efficiency can be realized. Furthermore, as the constitution is such that the respective parts such as thermal input part, gas tank, and generating unit, are all contained in the radiation part vessel, the whole generator can be dipped in water, so that a low priced, highly efficient water cooling system can be realized. In case of the water cooling system, it becomes unnecessary to supply power for driving radiation fan so as to arouse forced convection, and the electric power obtained by thermoelectric conversion can be wholly taken out externally.
In the embodiment of FIG. 11, the fuel tank is set at the top part of the thermal input part, but the same may be set at the lower part of the thermal input part. In such a case, because the exhaust gas is formed from the upper part, the exhaust gas pipe can be short, and piping is easy. Also, it is possible to arrange the fuel tank and the thermal input part in parallel in a radiation vessel.
Though FIG. 11 is an embodiment of a case where a pair of generating units are used, when constitution is made to arrange two pairs of generating units on four faces of the thermal input part, it is needless to say that a generator of higher output can be provided.
Moreover, if a removable cooling water vessel is installed outside the radiation part vessel, convenience is provided in moving the power source.
Alternatively, a fuel tank may be constituted by a heat resistant vessel and a structure to infuse a fuel gas may be adopted.

(Embodiment 2)

FIG. 13 is a sectional view showing the constitution of the thermoelectric generator according to Embodiment 2. In FIG. 13, the part 7 is a fuel tank, for which a commercialized butane gas cylinder for cassette burner is directly used. The fuel tank 37 is connected to the nozzle 38 and the throat part 39 which are the mixing means of fuel gas with air, through a gas tube 41. The fuel tank can be freely set in and outside the container, within the length of the gas tube 41. Other constitution is the same as in Embodiment 1.
The operation of the thermoelectric generator as constituted above is the same as in Embodiment 1.
According to this embodiment, by using a heat conductive end plate of comb shaped structure, a thermal input part of a type integral with the heat exchanger can be constituted, and accordingly, the catalytic combustion heat can be efficiently inputted to the high temperature side surface of the thermoelectric element. Also, as the heat conductive end plate and the catalyst part are in mutual contact, excessive rise of the surface temperature of the combustion part can be prevented to make it possible to realize a constitution suited for the heat resistance of the thermoelectric element.
Also, due to the constitution in which the fuel tank can be set externally, the fuel tank does not show temperature rise, and when it is adapted to the use such as AV power source, convenience and safety in fuel supply can be secured.
Furthermore, as a part of the gas tube and the nozzle and the throat part are contained in a head radiation vessel, the gas sent to the combustion part can be preheated, and efficient combustion can be realized.
Moreover, due to the constitution of all parts other than the gas tank being contained in the radiation vessel, the whole electric generator can be dipped in water, and cheap and highly efficient water cooling system can be realized. In case of the water cooling system, it becomes unnecessary to supply power for driving radiation fan so as to arouse forced convection, and the electric power obtained by thermoelectric conversion can be wholly taken out externally.
Also, when a removable cooling water tank is set on the outside of the radiator vessel, it becomes convenient in moving the power source.
Further, the fuel tank may be constituted by a heat resistant container, so as to permit infusion of fuel gas.

(Embodiment 3)

In FIG. 14, Embodiment 3 is shown. There is shown a constitution of a thermoelectric generator having a construction wherein a thermoelectric element or a pair of planar electric generation units 31 comprising thermoelectric elements are joined to both sides of the thermal input part 33, and held by a pair of heat radiation part 32 comprising heat conductive plates. The outer surface of the heat conductive plate of the radiator 32 has a fin shape so as to increase of the heat exchange area. On the outer surface of this radiator, there is installed a pair of removable cooling water tank 40, thereby making it possible to carry out either air cooling or water cooling. Also, in order to make it possible to install the fuel tank 37 on the body or to use it separated from the body, the nozzle part 8 and the fuel tank 9 are connected by a tube 41. Other structures are same as in Embodiment 1.
The operation of the generator of this constitution is the same as in Embodiment 1.
According to the constitution of this embodiment 3, by using a heat conductive end plate of comb shaped structure, a thermal input part of a type integral with the heat exchanger can be constituted, and accordingly, the catalytic combustion heat can be efficiently inputted to the high temperature side surface of the thermoelectric element. Also, as the heat conductive end plate and the catalyst part are in mutual contact, excessive rise of the surface temperature of the combustion part can be prevented to make it possible to realize a constitution suited for the heat resistance of the thermoelectric element.
Also, due to the constitution in which the fuel tank can be set externally, the fuel tank does not show temperature rise, and when it is adapted to the use such as AV power source which requires continuous supply of fuel, convenience and safety in fuel supply can be secured. Also, in FIG. 14, because the nozzle part or a mixing part of fuel gas with air is warmed by exhaust heat from the thermal input part, highly efficient combustion can be carried out. Efficient combustion can be realized.
As apparent from the above description, according to the second invention, thermal input of catalytic combustion heat to the thermoelectric element can be made in higher density, and highly efficient and cheap radiation in water cooling system can be realized without the driving power such as radiation fan. Thus, there can be provided compact and practical constitution of thermoelectric generator for outdoor use.

(C)

Next, the embodiments of the third invention will be explained with reference to FIG. 15 and FIG. 16.

(Embodiment 1)

FIG. 15(a) is a vertical sectional view of the thermoelectric generator of Embodiment 1 of the third invention, and FIG. 15(b) is a front view of the radiation part 60 of said thermoelectric generator. In FIG. 15(a), the part 51 is a planar electric generation unit made by connecting a pair of thermoelectric elements or a plurality of thermoelectric elements in series. It is held between the fin part 52 and the thermal input part 53, and installed on both sides of the thermal input part 53. The fin part 52 is an aluminum single plate having a large number of fins 52c on the outer surface of the disc shaped base plate. As shown in FIG. 15(b), at the central part 52a of the fin 52, the fin 52c is positioned low or does not exist, where a DC axial flow fan 54 is installed. The fin 52c is radially formed so that the compulsory air of the fan 54 flows radially from the center of the fan 54. The part 52b is a gap between them. The thermal input part 53 comprises a heat conductive combustion chamber 55 of aluminum material and a combustion part 56 installed inside the combustion chamber 55. It is desirable for the combustion chamber 55 to have a fin structure on the inner wall. The part 57 is a fuel tank, and is connected to the combustion chamber 55 through the nozzle 58 and the throat part 59.
With respect to the thermoelectric generator constituted as above, the operation thereof is explained as follows.
In FIG. 15, a commercialized butane gas is used as a fuel. The fuel gas jetted from the nozzle 58 becomes a mixed gas involving air, it is passed through the throat part 59, and burns in the combustion chamber 55. The produced exhaust gas is discharged outside the generator from the exhaust port on the upper part of the combustion chamber 55. The combustion heat obtained in the thermal input part 53 is supplied to the high temperature side surface of the thermoelectric element of the planar electric generation unit 51, and as the low temperature side of the thermoelectric element is in contact with the fin part 52, a temperature difference is formed between the high temperature side and the low temperature side of the thermoelectric element, and electric generation by thermoelectric power takes place. When the generation output reaches a size necessary for driving the fan 54, the fan 54 starts to rotate, the temperature difference formed on the thermoelectric element and the accompanied thermoelectric power increase, and in the meantime the power reaches the normal state.
When the electric generator of this embodiment is driven, it requires about 30 seconds until the two fans (DC 12V, 100 mA) come to start, and about 5 - 8 minutes until the output (15W) stabilizes. The surface temperature of the element at the time of the stabilization of output was 210°C on the high temperature side and 90°C on the low temperature side.
According to the present embodiment, because a radiation part 60 having a heat exchange fin part 52 and a fan part 54 formed in one-piece can be constituted, the volume of the radiation part 60 can be drastically constrained. Also, due to the constitution of leading the forced air radially from the central part of the fan 54 in the gap of the fin 52c, resistance by the fin 52 is decreased, and the air volume of fan can be increased. As a result, it has become possible to utilize the fan capacity to the maximum extent, leading to the improvement of performance of the radiation part 60. Simultaneously, the outlet temperature of the heat exchanged air can be suppressed to a low temperature, and safety can be secured.
In FIG. 15, there is adopted a constitution wherein a gas tank is installed at the bottom part of the generator, and the fuel gas is preheated with the heat from the fin part. However, in order to facilitate tank replacement or the like, the tank may be externally set. In such a case, it is desirable to make such constitution that the fuel gas can be preheated with the combustion heat or exhaust air heat before it is sent into the nozzle.
In the current experiment a butane gas is used as a fuel, but it is of course possible to use propane gas, natural gas, etc. In case of using a liquid fuel such as alcohols, the handling of the generator may become inconvenient, but it becomes unnecessary to use nozzle or throat, so that more simple constitution can be realized.
If, as a heat source in the thermal input part, catalytic combustion heat is utilized, planar uniform thermal input can be made, so that a generator having higher efficiency can be constituted. Alternatively, there may be constituted a generator as means for recovering a part of the waste heat by utilizing the waste heat of fuel battery or engine.

(Embodiment 2)

FIG. 16(a) is a vertical sectional side view showing the constitution of the heat radiation part 60 of the thermoelectric generator according to Embodiment 2 of the third invention, and FIG. 16(b) is a front view of the heat radiation part 60 of he thermoelectric generator thereof. In FIG. 16, the part 62 is an aluminum fin part, and 54 is a DC axial flow fan.
The part 61 is a motor part of the fan. The motor part 61 is buried in the fin 52 through the heat insulation layer 62. For the heat insulation layer 62, a ceramic material such as alumina wool can be used. A heat insulation layer may be provided by an air layer of about several millimeters.
The operation of the thermoelectric generator having the above constitution of the heat radiation part is the same as that of Embodiment 1, excepting the following points.
By the construction of providing a heat insulating layer 62 between the motor part 61 and the fin part 52, in the case of this embodiment, even when the temperature of the central part of the fin is 100°C, the motor part can be kept to 70°C or lower, so that the durability of the fan 54 can be improved.
Besides, even if the size and shape of the generator change, the present invention can be applied by making the thicknesses of the peripheral part and central part of the fin bottom plate or the thickness of the heat insulation layer optimum.
As described above, according to the third invention, in a thermoelectric generator utilizing as a heat source combustion heat or waste heat including catalytic combustion heat, it becomes possible to make compact constitution of highly efficient and durable heat radiation part, and accordingly it is possible to realize reduction in size and weight or elevation of performance of a thermoelectric generator.

Claims

A thermoelectric generator using catalytic combustion heat of fuel gas as a heat source, having a construction wherein a thermoelectric element or a planar electric generation unit comprising thermoelectric elements has a construction held between the thermal input part and the heat radiation part, having fuel gas supply means and means for mixing fuel gas with air, and having a structure that the combustion heat can be directly supplied to the thermoelectric element by burning the mixed gas of fuel with air in a catalyst part arranged in said thermal input part, said thermal input part having a heat conductive end plate and a catalyst part which are in contact with the thermoelectric element, the face opposite to said thermoelectric element of said heat conductive end plate having a structure of convex and concave configuration, and said catalyst part being constituted in said convex and concave configuration surface.
A thermoelectric generator using catalytic combustion heat of fuel gas as a heat source, being provided with a pair of thermoelectric elements or planar electric generation units comprising thermoelectric elements held between a thermal input part and a heat radiation part, in a structure to share said thermal input part, having fuel gas supply means, and means for mixing a fuel gas with air, and having a structure of being capable of directly supplying the combustion heat to said thermoelectric element by burning the mixed gas of fuel with air in a catalyst part arranged in said thermal input part, characterized in that said thermal input part comprises a heat conductive end plate and a catalyst part, a surface opposite to said thermoelectric element of said heat conductive end plate has convex and concave shaped structure, and said catalyst part is constituted on said convex and concave shaped surface.
A thermoelectric generator according to claim 1 or 2, wherein the catalyst part is a metal carried catalyst made by coating ceramic fine powder carried with precious metal catalyst on the surface of heat resistant metal thin plate having a thickness of no more than 0.5 mm, and said metal carried catalyst is constituted in a form of covering at least a part of said convex and concave shape.
A thermoelectric generator according to claim 1 or 2, wherein the catalyst part on the fuel gas inflow port side is less than the catalyst part on the fuel gas discharge side.
A thermoelectric generator according to claim 1 or 2, wherein the thickness of the heat conductive end plate varies in the direction of the fuel gas flow, and the thickness is large at the position in the vicinity of the fuel gas inflow port side.
A thermoelectric generator using catalytic combustion heat of fuel gas as a heat source, having a construction wherein a thermoelectric element or a planar electric generation unit comprising thermoelectric elements has a construction held between the thermal input part and the heat radiation part, having fuel gas supply means and means for mixing fuel gas with air, and having a structure that the combustion heat can be directly supplied to the thermoelectric element by burning the mixed gas of fuel with air in a catalyst part arranged in said thermal input part, characterized by having means for thermal recovery and simultaneously reducing the temperature of exhaust gas by making heat exchange between the exhaust gas from the thermal input part and the fuel before being supplied to said thermal input part.
A thermoelectric generator according to claim 6, wherein the fuel gas supply means are constituted by a tank for retaining a liquid fuel, an evaporation chamber for evaporating the liquid fuel in said tank, and a flow path for transporting the fuel from said tank to the evaporation chamber, and include means for carrying out thermal recovery and reducing the temperature of the exhaust gas, and accelerating the evaporation of the liquid fuel by heat exchanging the exhaust gas from said thermal input part with at least one of the liquid fuel in said tank, in an evaporation chamber, and in the flow path.
A thermoelectric generator using catalytic combustion heat of fuel gas as a heat source, having a construction wherein a thermoelectric element or a planar electric generation unit comprising thermoelectric elements has a construction held between the thermal input part and the heat radiation part, having fuel gas supply means and means for mixing fuel gas with air, and having a structure that the combustion heat can be directly supplied to the thermoelectric element by burning the mixed gas of fuel with air in a catalyst part arranged in said thermal input part, said means for mixing fuel gas with air being constituted by a nozzle for jetting a fuel gas and a throat part for sending the jetted fuel gas and the air mixed in the form of being involved in the fuel gas into the thermal input part, and being provided with means for carrying out thermal recovery by heat exchange between the exhaust gas from said thermal input part and the mixed gas passing in the throat part, and for reducing the temperature of the exhaust gas.
A thermoelectric generator using catalytic combustion heat of fuel gas as a heat source, having a construction wherein a thermoelectric element or a planar electric generation unit comprising thermoelectric elements has a construction held between the thermal input part and the heat radiation part, having fuel gas supply means and means for mixing fuel gas with air, and having a structure that the combustion heat can be directly supplied to the thermoelectric element by burning the mixed gas of fuel with air in a catalyst part arranged in said thermal input part, said means for mixing fuel gas with air being constituted by a nozzle for jetting a fuel gas and a throat part for sending the jetted fuel gas and the air mixed in the form of being involved in the fuel gas into the thermal input part, characterized in that the air to be mixed in the form of being involved in a fuel gas is the air which is heat exchanged by the exhaust gas from said thermal input part.
A thermoelectric generator comprising a thermal input part using the catalytic combustion heat of fuel gas as a heat source, a heat radiation part having a heat conductive container whose at least a part of the outer surface is of a fin shape, more than a pair of planar electric generation units held between the outer wall of said thermal input part and the inner wall of said heat radiation part, utilizing a thermoelectric element, fuel gas supply means including a fuel tank, and mixing means for mixing a fuel gas with air, said fuel gas supply means and said mixing means being installed in a heat conductive container in said heat radiation part, characterized by directly supplying the combustion heat to the thermoelectric element of said thermoelectric generation unit by burning the mixed gas of fuel with air in a catalyst part disposed in said thermal input part, and at the same time air cooling or water cooling said heat radiation part.
A thermoelectric generator comprising a thermal input part using the catalytic combustion heat of fuel gas as a heat source, a heat radiation part having a heat conductive container whose at least a part of the outer surface is of a fin shape, more than a pair of planar electric generation units held between the outer wall of said thermal input part and the inner wall of said heat radiation part, utilizing a thermoelectric element, a fuel tank, a fuel gas transporting means, and mixing means for mixing a fuel gas with air, said mixing means being installed in a heat conductive container in said heat radiation part, said fuel tank being freely installed in or out of the container, and connected to said mixing means through said fuel gas transporting means, characterized by directly supplying the combustion heat to the thermoelectric element by burning the mixed gas of fuel with air in a catalyst part disposed in said thermal input part, and air cooling or water cooling said heat radiation part.
A thermoelectric generator comprising a thermal input part using the catalytic combustion heat of fuel gas as a heat source, a heat radiation part constituted by a heat conductive plate whose at least a part of the outer surface is of a fin shape, a cooling water container provided outside said heat radiation pat, more than a pair of planar electric generation units held between the outer wall of said thermal input part and the inner wall of said heat radiation part, utilizing a thermal element, fuel gas supply means including a fuel tank, and mixing means for mixing a fuel gas with air, said fuel gas supply means and said mixing means being installed in a heat conductive container in said heat radiation part, characterized by directly supplying the combustion heat to said thermoelectric element of said thermoelectric generation unit by burning the mixed gas of fuel with air in a catalyst part disposed in said thermal input part, and water cooling said heat radiation part by supplying water to said cooling water container.
A thermoelectric generator according to claim 10, 11 or 12, wherein said thermal input part has a pair of oppositely disposed heat conductive end plates and said catalyst part, the inside wall surfaces of said oppositely disposed pair of heat conductive end plates form the comb-shaped heat exchange fins, said catalyst part is formed on the surface of the heat exchange fin, and a combustion chamber of a style to surround said catalyst part by said pair of heat conductive end plates is formed.
A thermoelectric generator comprising a thermal input part for inputting heat, a heat radiation part having a fin part and a fan, an electric generation unit held between said heat radiation part and said thermal input part for carrying out thermoelectric conversion by utilizing a thermoelectric element, and fuel supply means for supplying fuel, being designed to supply heat directly to the high temperature side of said thermoelectric element, simultaneously air cool the radiation part which is in contact with the radiation side of said thermoelectric element and carry out thermoelectric generation, characterized in that the whole or a part of said fan is stored in the fin part of said radiation part.
A thermoelectric generator according to claim 14, wherein the fins of the fin part are formed in radial disposition, and said fan is disposed on the central part of radiation where there is no fin or where the position is low.
A thermoelectric generator according to claim 14, wherein the fan is an axial flow fan, and heat insulation means are provided between the motor part of said fan and said fin part.